An aluminum anode foil formation solution and a formation method based on the same

Abstract

This invention discloses an aluminum anode foil forming solution and a forming method based on this solution, belonging to the field of aluminum electrolytic capacitor anode foil manufacturing technology. The aluminum anode foil forming solution contains acetylacetone salts, which are titanium acetylacetone, zirconium acetylacetone, or silver acetylacetone. The concentration of acetylacetone salts in the aluminum anode foil forming solution is 0.01~1 g / L. Formation based on this aluminum anode foil forming solution can be performed using a one-step forming process or a six-stage forming process. This invention adds acetylacetone salts with high dielectric constants to the anode foil forming solution, forming a high dielectric constant composite oxide film on the aluminum foil surface during the forming process, significantly improving the specific capacitance of the anode aluminum foil while reducing forming energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of aluminum electrolytic capacitor anode foil manufacturing technology, specifically relating to an aluminum anode foil forming solution and a forming method based on this forming solution. Background Technology

[0002] Aluminum electrolytic capacitors are indispensable key components in electronic products, with approximately 70% of their cost coming from the electrode aluminum foil, among which the anode aluminum foil plays a decisive role in the capacitor's capacitance. According to the capacitance calculation formula C=(ε0εr)S / d, ways to improve specific capacitance include increasing the specific surface area S, decreasing the oxide film thickness d, and increasing the relative permittivity εr of the dielectric. Traditional formation processes use inorganic acids such as boric acid, phosphoric acid, and adipic acid, or organic acids and their salts, as the formation solution. The resulting alumina dielectric layer has a permittivity of approximately 7.7, limiting further improvements in the anode foil's specific capacitance.

[0003] Some valve metal oxides (such as TiO2, ε) r =30-118; Zirconium dioxide (ZrO2), ε r =11-25; Ta2O5, ε r Oxides with dielectric constants of 25-45 are considered potential materials for replacing or reinforcing alumina dielectric layers. However, effectively introducing these high-dielectric-constant oxides into alumina dielectric layers to form stable composite structures remains a significant technical challenge. Existing technologies, such as physical methods like vapor deposition, sputtering, and molecular beam epitaxy, suffer from expensive equipment, high production costs, and complex processes, limiting their industrial application prospects. Chemical methods mainly focus on hydrolysis deposition and sol-gel methods; however, the hydrolysis deposition process is significantly affected by factors such as the pH, temperature, and concentration of the treatment solution, resulting in large fluctuations in the uniformity and density of the deposited film. The sol-gel method requires repeated immersion and drying cycles, leading to excessively long processing times and problems such as poor film uniformity, stability, adhesion, and susceptibility to cracking.

[0004] Acetylacetone salts are an important class of organometallic compounds with excellent complexing ability and thermal stability, and have been widely used in chemical, electronic, and materials science fields. Among them, titanium acetylacetone, zirconium acetylacetone, and silver acetylacetone, with their high dielectric constants, exhibit significantly higher dielectric properties than traditional alumina, providing a theoretical possibility for their application in formation solution systems. However, there are currently no reports on the use of acetylacetone salts in the aluminum anode foil formation process, indicating that this direction has significant potential for further exploration both academically and technically. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides an aluminum anode foil forming solution and a forming method based on the forming solution, which solves the problems of complex process, expensive equipment, poor uniformity, stability and adhesion of the film, and easy cracking of the film in the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is to provide an aluminum anode foil forming solution containing acetylacetone salt.

[0007] The beneficial effects of the above-mentioned technical solution of this invention are as follows: acetylacetone salt has the following functions in the formation solution: 1) Chelation effect: The acetylacetone group in acetylacetone salt can form a stable chelate with the valve metal ion, controlling the hydrolysis rate of the valve metal ion and preventing rapid hydrolysis to form a precipitate. The enol group of acetylacetone produces more OH than water. - It is more likely to undergo chelation reaction with valve metal ions, preventing the hydrolysis of valve metal ions and allowing alkoxy groups to be converted by OH groups in water. - 1) Slowing down the hydrolysis reaction due to substitution. 2) Film formation control: In addition to controlling the hydrolysis rate of valve metal ions, acetylacetone salts can also control the gelation time of the sol and the size of the colloidal particles. By adjusting the concentration of acetylacetone salts, the deposition thickness and nucleation density of the high-dielectric phase on the aluminum foil surface can be precisely controlled. 3) Formation of composite oxide film: During the anodic oxidation process, the valve metal ions generated by the decomposition of acetylacetone salts migrate to the aluminum foil surface under the action of an electric field and react with OH-. - The reaction generates valve metal hydroxides, which are then dehydrated after high-temperature heat treatment to form valve metal oxides with high dielectric constants (such as TiO2, ZrO2, Ag2O). These oxides are uniformly distributed in the Al2O3 oxide film, forming a composite oxide film with good compatibility, which significantly improves the dielectric constant of the oxide film.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the acetylacetone salt is titanium acetylacetone, zirconium acetylacetone, or silver acetylacetone.

[0010] Furthermore, the concentration of acetylacetone salt in the aluminum anode foil forming solution is 0.01~1 g / L.

[0011] Furthermore, the concentration of acetylacetone salt in the aluminum anode foil forming solution is 0.01~0.5 g / L.

[0012] Furthermore, a method for forming aluminum anode foil involves using the aforementioned anode foil forming solution for forming.

[0013] Furthermore, a one-step formation process is adopted for formation, and the aluminum anode foil formation solution also contains boric acid with a concentration of 50 g / L and a pH of 4-5.

[0014] Furthermore, the one-step formation process includes the following steps: (1) Pretreatment: Place the aluminum foil in a 95 ℃ water bath for 5 min; (2) Formation treatment: The pretreated aluminum foil is placed in the aluminum anode foil formation solution, and the current density is 80 mA / cm². 2 Anodizing was performed for 30 minutes at a voltage of 260 V. (3) Heat treatment: The aluminum foil after the formation treatment is calcined at 500 °C for 5 min; (4) Re-forming: The calcined aluminum foil is placed in a forming solution containing 50 g / L boric acid, and the forming is carried out at a temperature of 85℃ and a current density of 40 mA / cm². 2 Under a voltage of 260 V, the process was completed in 5 minutes. (5) Clean and dry the treated aluminum foil to obtain electrolytic foil.

[0015] Furthermore, a six-stage formation process is adopted, and the composition of the aluminum anode foil formation solution at each stage is as follows: The primary formation solution contains 3.5%–7% ammonium adipic acid, 0.2%–1.0% adipic acid, and 0.3–0.8 g / L acetylacetone. The secondary formation solution contains 1.5%~3.5% ammonium adipic acid, 0.1%~0.5% adipic acid, 0.5%~2% boric acid, and 0.2~0.5 g / L acetylacetone. The tertiary formation solution contains 0.05%~0.1% adipic acid, 1%~3% boric acid, 0.1% ammonium pentaborate, and 0.1~0.2 g / L acetylacetone. The fourth-stage formation solution contains 2%–4% boric acid, 0.1% ammonium pentaborate, and 0.05–0.1 g / L acetylacetone. The fifth-stage formation solution contains 3-6% boric acid, 0.2% ammonium pentaborate, and 0.01-0.02 g / L acetylacetone. The sixth-stage formation solution contains 4-8% boric acid and 0.3% ammonium pentaborate by mass.

[0016] Furthermore, the mass fraction of ammonium adipicate in the primary formation solution is 5%, the mass fraction of adipic acid is 0.6%, and the concentration of acetylacetone salt is 0.3~0.8 g / L; The secondary formation solution contains 2.5% ammonium adipic acid, 0.2% adipic acid, 1% boric acid, and 0.2-0.5 g / L acetylacetone. The mass fraction of adipic acid in the tertiary formation solution is 0.05%, the mass fraction of boric acid is 2%, the mass fraction of ammonium pentaborate is 0.1%, and the concentration of acetylacetone salt is 0.1~0.2 g / L; The mass fraction of boric acid in the fourth-stage formation solution is 3%, the mass fraction of ammonium pentaborate is 0.1%, and the concentration of acetylacetone salt is 0.05~0.1 g / L; The mass fraction of boric acid in the fifth-stage formation solution is 5%, the mass fraction of ammonium pentaborate is 0.2%, and the concentration of acetylacetone salt is 0.01~0.02 g / L; The mass fraction of boric acid in the sixth-stage formation solution is 6%, and the mass fraction of ammonium pentaborate is 0.3%.

[0017] Furthermore, the six-stage formation process includes the following steps: (1) Pretreatment: Place the aluminum foil in a 95 ℃ water bath for 5 min; (2) Multi-stage formation treatment: The pretreated aluminum foil is placed in each stage of the formation solution for anodizing treatment. The formation parameters for each stage are as follows: Primary formation: A primary formation solution was used, with a formation voltage of 160 V and a current density of 50 mA / cm². 2 The processing time was 10 minutes, and the temperature was 90 ℃. Two-stage formation: A two-stage formation solution was used, with a formation voltage of 240 V and a current density of 50 mA / cm². 2 The processing time was 10 minutes, and the temperature was 85 ℃. Three-stage formation: A three-stage formation solution is used, with a formation voltage of 320 V and a current density of 50 mA / cm². 2 The processing time was 15 minutes, and the temperature was 85 ℃. Four-stage formation: A four-stage formation solution is used, with a formation voltage of 400 V and a current density of 50 mA / cm². 2 The processing time was 10 minutes, and the temperature was 85 ℃. Five-stage formation: A five-stage formation solution is used, with a formation voltage of 480 V and a current density of 40 mA / cm². 2 The processing time is 100~300 s, and the temperature is 85 ℃; Six-stage formation: A six-stage formation solution was used, with a formation voltage of 520 V and a current density of 40 mA / cm². 2 The processing time is 100~300 s, and the temperature is 85 ℃; (3) Phosphorus treatment: The aluminum foil after the sixth-stage formation is placed in a phosphoric acid solution and treated at 40~60℃ for 5 minutes; (4) Heat treatment: The phosphorus-treated aluminum foil is subjected to rapid high-temperature annealing at 490~510 ℃; (5) Re-forming: The heat-treated aluminum foil is placed in a forming solution containing 4-8% boric acid and 0.3% ammonium pentaborate by mass for forming. The forming voltage is 520 V and the current density is 20 mA / cm. 2 The temperature was 85 ℃, and the reaction time was 5 min. (6) Secondary post-processing: Repeat steps (3) to (5) once; (7) Clean and dry the treated aluminum foil to obtain electrolytic foil.

[0018] The beneficial effects of this invention are: 1) Significantly improved specific capacity: By adding acetylacetone salt, a high dielectric constant composite oxide film is formed on the surface of the aluminum foil, increasing the specific capacity of the anode aluminum foil by 15%~30%. 2) Improved oxide film quality: The composite oxide film is dense and uniform, with controllable leakage current, and its withstand voltage performance meets the requirements of high-voltage forming foil. 3) Strong process compatibility: The method of this invention is simple, highly compatible with existing forming lines, and easy to implement for large-scale industrial production. 4) Environmentally friendly: Acetylacetone salt is an environmentally friendly reagent and may reduce energy consumption per unit product. Attached Figure Description

[0019] Figure 1 The images shown are scanning electron microscope (SEM) images of the aluminum foil prepared in Example 2-B, where A to C are images at magnifications of 2000, 7000, and 17000, respectively. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0021] Example 1: Screening and one-step formation process of acetylacetone salts (1) Prepare four groups of formation solutions. The base solution is an aqueous solution containing 50 g / L boric acid. The pH is adjusted to 4-5 with citric acid and ammonia, and the temperature is maintained at 85 °C. Different acetylacetone salts are added to the base solution respectively. Group 1-A: Added 0.5 g / L of titanium acetylacetonate; Group 1-B: Zirconium acetylacetonate 0.5 g / L was added; Group 1-C: Silver acetylacetone 0.5 g / L added; Group 1-D: No acetylacetone salts were added (blank control).

[0022] (2) Pretreatment: Take four sintered aluminum foils of the same specifications, immerse them in deionized water at 95 ℃ for 5 minutes to remove surface impurities, and then drain them.

[0023] (3) Primary formation treatment: The four pre-treated sintered aluminum foils were used as anodes and placed in the above-mentioned four formation solutions 1-A, 1-B, 1-C, and 1-D. Stainless steel was used as the cathode, and anodizing was performed under constant temperature conditions of 85 °C. The current density was controlled to be constant at 80 mA / cm. 2 After the voltage rises to 260 V, maintain this constant voltage for 30 minutes.

[0024] (4) Heat treatment: Take out the sintered aluminum foil after the formation treatment, clean it with deionized water, and calcine it in an air atmosphere at 500 °C for 5 min.

[0025] (5) Replenishment of the formation: The calcined aluminum foil is placed in a basic formation solution without additives (an aqueous solution containing 50 g / L boric acid, pH 4.5, 85 ℃), and the reaction is carried out at 85 ℃, a voltage of 260 V, and a current density of 40 mA / cm. 2 Under the condition of 5 minutes, the reaction time is increased.

[0026] (6) Clean and dry the treated aluminum foil to obtain electrolytic foil.

[0027] Performance testing and comparison: The specific capacity, leakage current, and withstand voltage of the four groups of treated electrolytic foils were tested, and the results are shown in Table 1.

[0028] Table 1. Performance of the samples obtained by the four groups of one-step formation processes.

[0029] As shown in Table 1, the test data showed that compared with the blank control group 1-D (1.29 μF / cm²), the results were significantly different. 2 Compared to the previous group, the three groups of samples 1-A, 1-B, and 1-C, which contained acetylacetone, showed a significant increase in specific volume, reaching 1.55, 1.68, and 1.58 μF / cm, respectively. 2Among them, zirconium acetylacetonate (group 1-B) showed the most significant improvement. This indicates that under experimental conditions, the addition of these acetylacetonate salts may effectively improve the effective dielectric constant and effective capacity per unit area of ​​the oxide film by altering its growth kinetics, microstructure, or dielectric properties. The boost time (Tr) is an important indicator for evaluating formation efficiency; a shorter time indicates a faster formation process. Data shows that the boost time for the blank group 1-D was 141 s, while the boost times for groups A, B, and C with added acetylacetonate salts were shortened to 118 s, 105 s, and 122 s, respectively. Group 1-B (containing Zr) had the shortest boost time, 36 s shorter than the blank group, resulting in an improvement in formation efficiency of approximately 25.5%. This indicates that the addition of acetylacetonate salts can accelerate the oxide film formation process and increase the formation rate.

[0030] The withstand voltage (Vt) of all samples was near the target value of 260 V, with the blank group 1-D at 267 V, groups 1-A and 1-B at 265 V, and group 1-C at 263 V. Although the addition of acetylacetone salt slightly reduced the withstand voltage, the decrease was within an acceptable range (1.5%-2.5%), and all samples met the requirements for high-voltage forming foil. This indicates that the addition of acetylacetone salt significantly improves the specific capacitance while having little impact on the insulation strength of the oxide film. Leakage current (LC) is a key indicator for evaluating the density and insulation performance of the oxide film; a lower value is better. The leakage current of the blank group 1-D was 21 μA / cm. 2 Group 1-A (including Ti) had a concentration of 22 μA / cm. 2 Group 1-B (containing Zr) had a concentration of 24 μA / cm. 2 Group 1-C (containing Ag) had a concentration of 28 μA / cm. 2 The leakage current of group 1-A (including Ti) is closest to that of the blank group, with an increase of only 1 μA / cm. 2 The leakage current of groups 1-B and 1-C increased by 3 μA / cm, respectively. 2 and 7 μA / cm 2 This indicates that titanium acetylacetonate performs better in maintaining low leakage current.

[0031] In terms of overall performance, zirconium acetylacetonate (group 1-B) showed the best performance in terms of specific capacity and boost time, with a 30.2% increase in specific capacity and a 25.5% reduction in boost time. Although the leakage current increased slightly, it remained within an acceptable range. Titanium acetylacetonate (group 1-A) excelled in maintaining low leakage current, with a 20.2% increase in specific capacity and only a 1 μA / cm increase in leakage current. 2 Although silver acetylacetonate (group 1-C) has a 22.5% increase in specific capacitance, its leakage current is significantly increased, resulting in relatively poor overall performance.

[0032] By adding acetylacetone salts during the aluminum anode foil formation process, a high-dielectric valve metal oxide is in-situ compositely generated on the aluminum foil surface simultaneously with the growth of an Al2O3 film via a one-step electrochemical synthesis method, combining the "synthesis" and "film formation" steps into one. Relying on the chelating and controlled release characteristics of acetylacetone salts (such as the advantages of zirconium acetylacetone in hydrolysis rate and thermal stability), uniform doping of valve metal ions and densification of the composite oxide film can be achieved. Zirconium acetylacetonate (ZrO2) performs best among the three, with the following technical advantages: 1) Excellent dielectric properties: The dielectric constant of ZrO2 is between 11 and 15, which is higher than that of Al2O3 (approximately 7.7). ZrO2 also has good thermal and chemical stability and is not easily decomposed during high-temperature heat treatment; 2) Good film quality: ZrO2 and Al2O3 have good lattice matching, resulting in a dense and uniform composite oxide film on the aluminum foil surface with low defect density and low leakage current; 3) High chelation stability: The chelation stability of ZrO2 in aqueous solution is better than that of titanium acetylacetonate and silver acetylacetonate. The hydrolysis rate is moderate, which is conducive to the formation of a uniform ZrO2 deposition layer on the aluminum foil surface.

[0033] Example 2: Multi-stage formation process based on zirconium acetylacetonate Based on the preferred results of Example 1, zirconium acetylacetone was added to the forming solution, and a multi-stage forming process was carried out to investigate its effect on the overall performance of the formed foil. The specific experimental procedure is as follows: (1) Pretreatment: Select four sintered aluminum foils from the same batch and of the same specifications, immerse them in deionized water at 95 ℃ for 5 min, and then drain them.

[0034] (2) Multi-stage formation treatment: The pretreated aluminum foil is placed in each stage of the formation solution for anodizing treatment. The formation parameters for each stage are as follows: Group 2-A (high concentration of zirconium acetylacetonate): ① Primary formation: The formation solution is an aqueous solution containing 5% (mass fraction) ammonium adipate, 0.6% (mass fraction) adipic acid, and 0.8 g / L zirconium acetylacetonate. The formation voltage is 160 V, and the current density is 50 mA / cm². 2 The time was 10 minutes and the temperature was 90 ℃.

[0035] ② Secondary formation: The formation solution is an aqueous solution containing 2.5% (mass fraction) ammonium adipate, 0.2% (mass fraction) adipic acid, 1% (mass fraction) boric acid, and 0.5 g / L zirconium acetylacetonate. The formation voltage is 240 V, and the current density is 50 mA / cm². 2 The time was 10 minutes and the temperature was 85 ℃.

[0036] ③ Three-stage formation: The formation solution is an aqueous solution containing 0.05% (mass fraction) adipic acid, 2% (mass fraction) boric acid, 0.1% (mass fraction) ammonium pentaborate, and 0.2 g / L zirconium acetylacetonate. The formation voltage is 320 V, and the current density is 50 mA / cm². 2 The time was 15 minutes and the temperature was 85 ℃.

[0037] ④ Fourth-stage formation: The formation solution is an aqueous solution containing 3% boric acid (mass fraction), 0.1% ammonium pentaborate (mass fraction), and 0.1 g / L zirconium acetylacetonate. The formation voltage is 400 V, and the current density is 50 mA / cm². 2 The time was 10 minutes and the temperature was 85℃.

[0038] ⑤ Fifth-stage formation: The formation solution is an aqueous solution containing 5% (mass fraction) boric acid, 0.2% (mass fraction) ammonium pentaborate, and 0.02 g / L zirconium acetylacetonate. The formation voltage is 480 V, and the current density is 40 mA / cm². 2 The time was 200 seconds and the temperature was 85℃.

[0039] ⑥ Sixth-stage formation: The formation solution is an aqueous solution containing 6% (mass fraction) boric acid and 0.3% (mass fraction) ammonium pentaborate. The formation voltage is 520 V and the current density is 40 mA / cm². 2 The time was 200 seconds and the temperature was 85 ℃.

[0040] Group 2-B (medium concentration of zirconium acetylacetone): 0.5 g / L was added to the first-stage formation solution, 0.3 g / L to the second-stage formation solution, 0.15 g / L to the third-stage formation solution, 0.08 g / L to the fourth-stage formation solution, 0.015 g / L to the fifth-stage formation solution, and no addition was made to the sixth-stage solution; the other conditions were the same as those in Group 2-A.

[0041] Group 2-C (low concentration of zirconium acetylacetonate): 0.3 g / L for primary formation, 0.2 g / L for secondary formation, 0.1 g / L for tertiary formation, 0.05 g / L for quaternary formation, 0.01 g / L for quinary formation, and no addition for septal formation; other conditions are the same as Group 2-A.

[0042] Group 2-D (zero concentration control group): No zirconium acetylacetone was added to any of the formation solutions, and other conditions were the same as those in Group 2-A, serving as a control for the traditional process.

[0043] Four sintered aluminum foils were used as anodes and placed in the forming solutions of the four formulations corresponding to 2-A, 2-B, 2-C, and 2-D. Formation was carried out according to the above steps, and each stage of formation was rinsed lightly with deionized water.

[0044] (3) Phosphorus treatment: The aluminum foil after the sixth-stage formation is placed in a 3% phosphoric acid solution and treated at 50 °C for 5 min to dissolve the unstable water components on the outer layer of the oxide film.

[0045] (4) Heat treatment: The phosphorus-treated aluminum foil is subjected to rapid high-temperature annealing in air atmosphere at 500 °C to dehydrate the hydrate and transform it into γ-Al2O3 or γ'-Al2O3 crystalline oxide, thereby reducing leakage current.

[0046] (5) Supplementary formation: The heat-treated aluminum foil is placed in the basic formation solution (an aqueous solution containing 6% boric acid and 0.3% ammonium pentaborate by mass), with a formation voltage of 520 V and a current density of 20 mA / cm². 2 The temperature was 85℃ and the reaction time was 5 min.

[0047] (6) Secondary post-processing: Repeat steps (3) to (5) once.

[0048] (7) The treated sample is cleaned with deionized water and dried in an oven at 80 ℃ to obtain the final electroplated foil sample.

[0049] The scanning electron microscope (SEM) image of the electroformed aluminum foil prepared in Example 2-B is shown below. Figure 1 As shown, under low magnification (A), the surface of the aluminum foil is composed of a large number of spherical or near-spherical particles of submicron to several micrometer size that are densely packed together, forming a porous basic morphology. After being magnified to high magnification (B) and (C), the dense and rough dielectric layer morphology of the surface of individual particles can be clearly observed.

[0050] Performance testing: In addition to routine tests, the formed foil samples were placed in deionized water at approximately 95 °C and boiled continuously for 60 minutes before being removed, dried, and tested for pressure resistance. The test results of the formed foil samples obtained in the experimental and control groups are shown in Table 2.

[0051] Table 2 Test results of samples obtained by multi-stage formation process

[0052] The specific capacities of the experimental groups with added zirconium acetylacetonate (2-A, 2-B, and 2-C) were significantly higher than those of the traditional control group 2-D. The specific capacities decreased with decreasing zirconium acetylacetonate concentration; the high-concentration group (2-A) had the highest specific capacity (1.12 μF / cm³). 2 The concentrations were significantly higher than those in the control group without additives (2-D, 0.88 μF / cm). 2The results indicate that the addition of zirconium acetylacetonate can effectively improve the dielectric constant of the dielectric oxide film or optimize its microstructure, thereby increasing the capacitance per unit area. The specific capacitance of medium concentration (2-B) is close to that of high concentration (2-A), indicating that within a certain concentration range, the improvement in specific capacitance tends to saturate.

[0053] The presence of zirconium acetylacetonate significantly shortens the pressure rise time (Tr). Regarding process efficiency, the addition of zirconium acetylacetonate significantly shortens Tr; the longest Tr (130 s) is observed without addition, while Tr is reduced to 105–110 s after addition. This is because zirconium acetylacetonate promotes oxide film formation efficiency and improves film formation kinetics.

[0054] Zirconium acetylacetonate has a certain influence on the dielectric strength and stability of the oxide film. With increasing zirconium acetylacetonate concentration, the initial breakdown voltage (Vt) decreases slightly, while the leakage current (LC) increases accordingly. The high-concentration group (2-A) exhibits the highest leakage current (28 μA / cm). 2 The 2-D group showed the largest decrease in withstand voltage (Vt60) after boiling in water for 60 min (a decrease of 11 V), indicating that excessive zirconium acetylacetonate may reduce the film density and affect its long-term stability under high temperature and humidity conditions. The unadded 2-D group had the highest withstand voltage (534 V), while all added groups had slightly lower withstand voltages (511~530 V). This may be because zirconium acetylacetonate alters the structure of the oxide film, causing a slight decrease in its dielectric strength, although it remains at a high level. Higher zirconium acetylacetonate concentrations resulted in greater leakage current; the 2-A group had the largest leakage current (28 μA / cm). 2 The lowest value was found in group 2-D (16 μA / cm). 2 This indicates that high concentrations of zirconium acetylacetonate may introduce more defects or slightly reduce the film's density, increasing leakage pathways. The withstand voltage (Vt60) after 60 min of boiling in water is a key indicator for evaluating the long-term stability and hydration resistance of the oxide film. Groups 2-B (medium concentration) and 2-C (low concentration) performed best, exhibiting extremely high withstand voltage retention rates and minimal differences from the initial withstand voltage after 60 min of boiling (only a decrease of 4 V and 6 V, respectively). Conversely, group 2-A (high concentration) showed a significant decrease in withstand voltage after 60 min of boiling (a decrease of 11 V), exhibiting the most significant performance degradation. Group 2-D, without additives, already had high withstand voltage, but it also decreased by 5 V after boiling.

[0055] Considering all performance parameters, the medium concentration group (2-B) achieves the best balance between specific volume, efficiency, and stability: its specific volume is close to that of the high concentration group, its boost time is short, and its leakage current is controllable (20 μA / cm). 2 Furthermore, it exhibits the best pressure resistance retention after boiling in water (with a decrease of only 4V). Therefore, within the framework of a multi-stage formation process, using the median concentration of zirconium acetylacetonate (i.e., the concentration gradient of group 2-B) is the optimal choice.

[0056] In summary, acetylacetone salts are used to generate high-dielectric valve metal oxides through in-situ composite formation, optimizing the oxide film. Among these, the zirconium oxide and alumina films generated by acetylacetone exhibit the best compatibility, resulting in a more uniform composite oxide film compared to other valve metals. This invention achieves in-situ composite formation of high-dielectric phases, directly increasing the dielectric constant of the dielectric layer and achieving a specific capacity increase of 15%–30%. This invention can be directly integrated into existing formation lines (industrial formation), requiring only the addition of trace amounts of acetylacetone salts (concentration 0.01–1 g / L) to each stage of the formation solution, significantly lowering the industrialization threshold.

[0057] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. An aluminum anode foil forming solution, characterized in that, The aluminum anode foil forming solution contains acetylacetone salt.

2. The aluminum anode foil forming solution according to claim 1, characterized in that: The acetylacetone salt is titanium acetylacetone, zirconium acetylacetone, or silver acetylacetone.

3. The aluminum anode foil forming solution according to claim 2, characterized in that: The concentration of acetylacetone salt in the aluminum anode foil forming solution is 0.01~1 g / L.

4. The aluminum anode foil forming solution according to claim 3, characterized in that: The concentration of acetylacetone salt in the aluminum anode foil forming solution is 0.01~0.5 g / L.

5. A method for forming aluminum anode foil, characterized in that: The anode foil forming solution according to any one of claims 1 to 4 is used for forming.

6. The method for forming aluminum anode foil according to claim 5, characterized in that: The anode foil is formed using a one-step formation process, and the anode foil formation solution also contains boric acid at a concentration of 50 g / L and a pH of 4-5.

7. The method for forming aluminum anode foil according to claim 6, characterized in that, The one-step formation process includes the following steps: (1) Pretreatment: Place the aluminum foil in a 95 ℃ water bath for 5 min; (2) Formation treatment: The pretreated aluminum foil is placed in the aluminum anode foil formation solution, and the current density is 80 mA / cm². 2 Anodizing was performed for 30 minutes at a voltage of 260 V. (3) Heat treatment: The aluminum foil after the formation treatment is calcined at 500 °C for 5 min; (4) Re-forming: The calcined aluminum foil is placed in a forming solution containing 50 g / L boric acid, and the forming is carried out at a temperature of 85 °C and a current density of 40 mA / cm². 2 Under a voltage of 260 V, the process was completed in 5 minutes. (5) Clean and dry the treated aluminum foil to obtain electrolytic foil.

8. The method for forming aluminum anode foil according to claim 5, characterized in that: The six-stage formation process is employed, and the composition of the aluminum anode foil formation solution at each stage is as follows: The primary formation solution contains 3.5%–7% ammonium adipic acid, 0.2%–1.0% adipic acid, and 0.3–0.8 g / L acetylacetone. The secondary formation solution contains 1.5%~3.5% ammonium adipic acid, 0.1%~0.5% adipic acid, 0.5%~2% boric acid, and 0.2~0.5 g / L acetylacetone. The tertiary formation solution contains 0.05%~0.1% adipic acid, 1%~3% boric acid, 0.1% ammonium pentaborate, and 0.1~0.2 g / L acetylacetone. The fourth-stage formation solution contains 2%–4% boric acid, 0.1% ammonium pentaborate, and 0.05–0.1 g / L acetylacetone. The fifth-stage formation solution contains 3-6% boric acid, 0.2% ammonium pentaborate, and 0.01-0.02 g / L acetylacetone. The sixth-stage formation solution contains 4-8% boric acid and 0.3% ammonium pentaborate by mass.

9. The method for forming aluminum anode foil according to claim 8, characterized in that: The primary formation solution contains 5% ammonium adipic acid, 0.6% adipic acid, and 0.3-0.8 g / L acetylacetone. The secondary formation solution contains 2.5% ammonium adipic acid, 0.2% adipic acid, 1% boric acid, and 0.2-0.5 g / L acetylacetone. The tertiary formation solution contains 0.05% adipic acid, 2% boric acid, 0.1% ammonium pentaborate, and 0.1-0.2 g / L acetylacetone. The fourth-stage formation solution contains 3% boric acid, 0.1% ammonium pentaborate, and 0.05-0.1 g / L acetylacetone. The boric acid in the five-stage formation solution has a mass fraction of 5%, the ammonium pentaborate has a mass fraction of 0.2%, and the concentration of acetylacetone salt is 0.01~0.02 g / L; The boric acid in the sixth-stage formation solution has a mass fraction of 6%, and the ammonium pentaborate has a mass fraction of 0.3%.

10. The method for forming aluminum anode foil according to claim 9, characterized in that: The six-stage formation process includes the following steps: (1) Pretreatment: Place the aluminum foil in a 95 ℃ water bath for 5 min; (2) Multi-stage formation treatment: The pretreated aluminum foil is placed in each stage of the formation solution for anodizing treatment. The formation parameters for each stage are as follows: Primary formation: A primary formation solution was used, with a formation voltage of 160 V and a current density of 50 mA / cm². 2 The processing time was 10 minutes, and the temperature was 90 ℃. Two-stage formation: A two-stage formation solution was used, with a formation voltage of 240 V and a current density of 50 mA / cm². 2 The processing time was 10 minutes, and the temperature was 85 ℃. Three-stage formation: A three-stage formation solution is used, with a formation voltage of 320 V and a current density of 50 mA / cm². 2 The processing time was 15 minutes, and the temperature was 85 ℃. Four-stage formation: A four-stage formation solution is used, with a formation voltage of 400 V and a current density of 50 mA / cm². 2 The processing time was 10 minutes, and the temperature was 85 ℃. Five-stage formation: A five-stage formation solution is used, with a formation voltage of 480 V and a current density of 40 mA / cm². 2 The processing time is 100~300 s, and the temperature is 85 ℃; Six-stage formation: A six-stage formation solution was used, with a formation voltage of 520 V and a current density of 40 mA / cm². 2 The processing time is 100~300 s, and the temperature is 85 ℃; (3) Phosphorus treatment: The aluminum foil after the sixth-stage formation is placed in a phosphoric acid solution and treated at 40~60℃ for 5 min; (4) Heat treatment: The phosphorus-treated aluminum foil is subjected to rapid high-temperature annealing at 490~510 ℃; (5) Re-forming: The heat-treated aluminum foil is placed in a forming solution containing 4-8% boric acid and 0.3% ammonium pentaborate by mass for forming. The forming voltage is 520 V and the current density is 20 mA / cm. 2 The temperature was 85 ℃, and the reaction time was 5 min. (6) Secondary post-processing: Repeat steps (3) to (5) once; (7) Clean and dry the treated aluminum foil to obtain electrolytic foil.

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